This invention relates to a liquid remoistenable adhesive composition having superior non-blocking properties at high temperature and high humidity and comprises water and a selected combination of partially hydrolyzed polyvinyl alcohol and a chemically inert, non-thermoplastic, cold water insoluble, particulate additive which is compatible and dispersible with an aqueous solution of the polyvinyl alcohol.
Remoistenable adhesives are commonly utilized in the production of envelopes, stamps, wallpaper, tapes, labels and similar products wherein it is desired to provide a dry adhesive film which on being moistened with water will become tacky and thereby allow for the ready adhesion to a chosen substrate. In the manufacture of remoistenable adhesive products, typically an aqueous solution or dispersion, or an organic solvent solution of the dry adhesive material is applied as a wet film to a substrate. After the water or organic solvent is removed by drying and evaporation, the resulting dry adhesive film will, on being moistened, produce the desired tacky adhesive surface.
The ability to provide an adhesive which is remoistenable is not in itself difficult and in fact there are a number of known and commercially available products that are used in various applications requiring a remoistenable adhesive. Some of the known remoistenable adhesive formulations include dextrin solutions (dextrin gums); a dextrin solution plus a water based emulsion of polymers such as polyvinyl acetate or ethylene vinyl acetate as disclosed in U.S. Pat. Nos. 4,575,525 issued Mar. 11, 1986 and 4,678,824 issued Jul. 7, 1987; and a polyvinyl alcohol solution combined with an emulsion of polymers such as polyvinyl acetate or ethylene vinyl acetate as shown in U.S. Pat. No. 2,850,468 issued Sep. 2, 1958.
The usefulness of a particular composition as a remoistenable adhesive in a specific application will depend on its ability to meet the many physical and chemical property requirements and to best satisfy the processing conditions to which it is subjected. Accordingly, a remoistenable adhesive composition in addition to providing good adhesion and remoistenability, typically is expected to provide a lay flat or non-curl product, satisfy processing conditions of different manufacturing equipment, provide adequate drying speed, resist hygroscopic blocking and satisfy various other requirements depending on the application involved.
The needs of the various applications requiring the use of a remoistenable adhesive have generally been met by different known formulations, such as noted above, as well as various modifications thereof. However, changing operating equipment and processes and increased customer requirements dictate the need for an improved remoistening adhesive which has desired properties at both high temperature and high humidity. Such a product is especially needed in the manufacture of stamps and envelopes where resistance to hygroscopic blocking and thermoplastic blocking is required under high temperature and high humidity conditions.